The present invention relates to the temporary blocking of the bore in a pipe through which a fluid flows and is particularly directed to the temporary blocking of mains carrying natural gas.
Where repairs to a section of a gas main are to be carried out or where a section of the main is to be partially or completely replaced it is frequently necessary temporarily to block the bore or main at a point or points upstream of the section. This prevents the flow of gas to the section of the main downstream of the blockage so that the necessary work can be carried out.
At present such temporary blockage is performed with the aid of an expansible bag of the type having an innermost inflatable bladder usually of rubber contained with an outermost protective bag of nylon or some such similar material. In use of such bags, a hole is drilled in the wall of the main and the bag is inserted into the main by way of an insertion device in the form of a sealable tube which is temporarily securable in the hole so drilled. Once inside the main the inner bladder is inflated by a supply of pressurised gas e.g. compressed air, by way of a pipe connected to the mouth of the bag, the pipe also providing means for locating the bag inside the main through the insertion tube which forms a gas-tight seal around the pipe.
Inflation of the bladder causes it to expand and force the outer bag to engage with the inner wall of the main to form a seal against the wall of the main.
The bag is removed by deflating the bladder and then withdrawing the pipe from the main via the hole and the insertion tube.
Unfortunately the outer protective bag and even the inner bladder are frequently ripped or torn as they are withdrawn from the main. This renders the bag totally unservicable and it is not an uncommon occurrence that such bags are irreparably damaged after Just one operation. Since these bags are relatively expensive, the overall cost of the repairs or replacement operations is increased owing to the wastage of such bags.